Abstract
Large scale earthquake of Mg 6.8 (on 23rd Oct.) and a series of aftershocks more than Mg 6 in a scale occurred in Chuetsu, Niigata Pref., Central Japan, in the end of October. It severely damaged allover the hill and caused enormous landslides. This study clarified the distribution of the landslides by aerial photo interpretation. Characteristics of landslide in this study area are summarized as follows;
1) Landslides of rotational or translational slide type, wider than 1 hectare, are concentrated in a NNE-SSW belt between Imo River and Shiotani River. It just coincides with a synclinal zone named Kajikane syncline (Fig. 2). It has been filled with sand stone or alternatives of sand and mud/silt stones overlaying mudstone. Imo River incises sand dominant area in eastern wing of the syncline. Their landslide masses consist of sand layers and they slid down on a westward dip slope consisted of mudstone. They are dip slope landslides. However, they are not landslides of primary movement. Many of them reactivated due to earthquake tremor within trans-accumulation areas of previous landslides.
2) Topographic feature in the western part of this study area is Questa. Westward gentle slope and eastward steep slope alternately develop in the western wing of Higashiyama Anticline that characterizes the outline of landform in this study area. Shallow sheeted slope failures are widely distributed on eastward anti-dip slopes. Detritus from slope failure turned to high speed debris flows, capturing reservoir water on the way.
